1. Field of the Invention
The present invention relates to a vehicle navigator which can calculate a vehicle running distance by using output data of an accelerometer
2. Description of the Related Art
A conventional vehicle navigator will be described with reference to FIGS. 7 to 10.
FIG. 7 is a block diagram showing the structure of a conventional vehicle navigator. In FIG. 7, reference numeral 101 represents an acceleration sensor for detecting an acceleration of a vehicle along its running direction. Reference numeral 102 represents a gyro sensor for detecting an angular velocity of a vehicle along its yawing direction. Reference numeral 107 represents a running distance calculator for calculating a vehicle running distance in accordance with output data of the acceleration sensor 10. Reference numeral 108 represents a running azimuth calculator for calculating a vehicle running azimuth in accordance with output data of the gyro sensor 102. Reference numeral 109 represents an arithmetic unit for calculating the position of a vehicle in accordance with the calculation results given by the running distance calculator 107 and the running azimuth calculator 108.
Reference numeral 104 represents a map storage for storing map data, and reference numeral 105 represents a display unit with a display screen. Reference numeral 106 represents a controller for receiving vehicle position information of the arithmetic unit 109, reading map data of a predetermined area from the map storage 104, and displaying the map data together with the position of a vehicle 100 (shown in FIG. 8) on the display unit 105.
FIG. 8 shows a coordinate system of a vehicle. As shown in FIG. 8, an X-axis is along the running direction of the vehicle 100 in the horizontal plane, a Y-axis is along the direction perpendicular to the X-axis in the horizontal plane, and a Z-axis is along the gravitational direction of the vehicle 100. In the following description, the motion of the vehicle 100 about the X-axis is called as a roll operation, and an angle of the rotation of the vehicle 100 caused by the roll operation is called as a roll angle .theta..sub.x. Similarly, the motion of the vehicle 100 about the Y-axis is called as a pitch operation, and an angle of the rotation of the vehicle 100 caused by the pitch operation is called as a pitch angle .theta..sub.y. The motion of the vehicle 100 about the Z-axis is called as a yaw operation, and an angle of the rotation of the vehicle 100 caused by the yaw operation is called as a yaw angle .theta..sub.x. The yaw angle .theta..sub.z represents a change of the running direction of a vehicle 100, and is also called as a running azimuth .theta..sub.z.
The operation of determining a position of the vehicle 100 having the vehicle navigator constructed as above will be described in which the position of a vehicle 100 is calculated by the arithmetic unit 109 in accordance with output data from the acceleration sensor 101 and gyro sensor 102.
At a predetermined time interval .DELTA.t, data is output from the acceleration sensor 101 and gyro sensor 102 to the arithmetic unit 109. The arithmetic unit 109 converts output data of the acceleration sensor 101 into an acceleration A.sub.x (i) and converts output data of the gyro sensor 102 into an angular velocity .omega..sub.x (i).
First, the running distance calculator 107 supplied with the acceleration A.sub.x (i) calculates a velocity V.sub.x (n) of the vehicle 100 by the equation (1) where the velocity at time n is V.sub.x (n), the acceleration at time i is A.sub.x i, a time interval of obtaining output data of the acceleration sensor 101 is .DELTA.t, and the initial velocity is V.sub.x (O). ##EQU1##
As the velocity V.sub.x (n) of the vehicle 100 at the time n is calculated by the equation (1), the running distance calculator 107 calculates a running distance .DELTA.D(n) of the vehicle at the time interval .DELTA.t by the equation (2). EQU .DELTA.D(x)=V.sub.x (n-1).multidot..DELTA.t+0.5.multidot.A.sub.x (n).multidot..DELTA.t.sup.2 (2)
The running azimuth calculator 108 supplied with the angular velocity .omega..sub.x (i) calculates the running azimuth .theta..sub.x (n) of the vehicle at the time n by the equation (3). ##EQU2##
When the running distance .DELTA.D(n) and running azimuth .theta..sub.x (n) at the time n are supplied from the running distance calculator 107 and running azimuth calculator 108 respectively, the arithmetic unit 109 executes a cumulative calculation starting from the initial position (X(0), Y(0)) as illustrated in FIG. 9 by using the equations (4) and (5), to thereby obtain the position (X(n), Y(n)) at the time n. ##EQU3##
As the position (X(n), Y(n)) of the vehicle 100 is obtained, the controller 106 marks the position of the vehicle 100 on map data supplied from the map storage 104, if necessary, by converting the position of the vehicle 100 into the coordinate system of the map data, and outputs it.
With the conventional vehicle navigator as mentioned above the running distance of the vehicle 100 is calculated by using the acceleration sensor 101. However, for example, in the case of a sloped road such as shown in FIG. 10 the acceleration A.sub.x (i) detected with the acceleration sensor 101 contains the running direction component of the gravitational acceleration G in addition to an acceleration a.sub.x (i) of the vehicle 100. Therefore, a correct acceleration of the vehicle 100 cannot be obtained. From this reason, an additional acceleration sensor, gyro sensor, or the like has been used conventionally to detect the pitch angle .theta..sub.y (i) of the vehicles to calculate the running direction components of the gravitational acceleration. In this manner, the running direction component of the gravitational acceleration G is removed from the acceleration A.sub.x (i) detected with the acceleration sensor 101. With this method, however, the number of acceleration sensors or gyro sensors increases and the apparatus becomes expensive.